Traditionally, coronary artery bypass graft (CABG) surgery has been performed through a median sternotomy, which is a hole in the middle of the chest. This involves sawing the sternum, or breast bone, in half longitudinally, thereby opening the chest. A standard 30-cm median sternotomy incision has been referred to as a "manhole" incision. Beginning around 1996, cardiac surgeons began performing minimally invasive CABG.
Minimally invasive techniques use an approximately 8-cm incision "keyhole" in the fourth intercostal space, the space between the fourth and fifth ribs.
There are two primary types of minimally invasive cardiac surgery: (1) minimally invasive direct coronary artery bypass (MIDCAB), which is performed while the heart is still beating; and (2) the port-access operation, performed on an arrested heart with the use of cardiopulmonary bypass and pharmacologic cardioplegia (i.e., using potassium chloride to temporarily stop the heart from beating).
When cardiac surgery is performed on an arrested heart, blood is pumped through the body and oxygenated by an external machine, the cardiopulmonary bypass pump. This machine takes deoxygenated blood from the systemic venous system, oxygenates the blood through a semipermeable membrane, and returns this oxygenated blood to the systemic arterial circulation. This mechanism effectively bypasses the lungs, which are the normal means for oxygenating blood. In the standard CABG procedure, access to the systemic venous circulation is made through a cannula (a thin, hollow tube) inserted into the right atrium or closely related structure, such as the superior vena cava (the large vein returning blood to the heart from the head and arms). Access to the systemic arterial circulation is made through a cannula inserted into the aorta (the largest artery in the body), which carries blood away from the heart and to the body. The surgeon also cross clamps the aorta around the level of the aortic arch (near the heart).
By contrast, in minimally invasive CABG procedures, a physician accesses the systemic venous circulation through a cannula inserted into the femoral vein at the level of the groin, and the physician accesses the systemic arterial circulation through a cannula inserted into the femoral artery. The latter cannula is guided through the femoral artery superiorly, up to the aortic arch. At the tip of this aortic cannula, an endo-aortic balloon is inflated to occlude the aorta from within. This balloon inflation serves the same purpose as the aortic cross-clamping performed in standard CABG procedures.
In methods of CABG that are entirely endoscopic, the surgeon makes two or three small (e.g., 2-cm) incisions in the chest for placement of an endoscope and surgical instruments.
To become proficient with any of these surgical techniques, especially the endoscopic techniques, requires practice. Cadavers can sometimes be used to practice surgery, but they are in short supply and expensive. Also, because cadavers do not bleed, it is hard to tell if surgical anastomoses have been performed successfully. There is thus a need for alternative ways to become proficient in the endoscopic cardiac surgery.